Sudden cardiac death kills 300,000 people in the United States yearly. More than half of these deaths are caused by arrhythmias including ventricular tachycardia. Currently there is no safe, effective and inexpensive method for treating most ventricular tachycardias. Thermal ablation using radiofrequency or laser heating can effectively treat supraventricular tachycardia, but the lesions are too small to treat most VTs, especially those that originate from infarct scars. Two effects limit the lesion size. First, the energy is absorbed in a thin layer of tissue surrounding the therapy tool. Second, thermal conduction is too small to carry the energy deeper into the tissue. We have developed saline-enhanced ablation, which uses infusion of warm saline through the myocardium (simultaneous with the application of heating energy) to increase the tissue thermal transport by a factor of 20 or more. We have shown that this method can increase the volume of thermal lesions in liver cancer by a factor of l00. We will adapt our system to test the improvement it provides to RF and laser heating of myocardium. The method that creates the largest, deepest lesions will be used for continued development in Phase 2. PROPOSED COMMERCIAL APPLICATIONS: The goal of this project is to develop a system and associated therapy protocols that can safely heat large regions of myocardium. This will be useful for treating ventricular tachycardia, especially VT following myocardial infarction, which typically requires large ablation lesions.